This invention relates to stabilizer compositions for halogen-containing vinyl polymers, the stabilized halogen-containing vinyl polymer compositions, and articles formed therefrom, and methods for stabilizing halogen-containing vinyl polymers.
Halogen-containing vinyl polymers, for example, poly(vinyl chloride) (PVC), copolymers of vinyl chloride and vinyl acetate, and poly(vinylidine chloride), are commonly used for fabricating a variety of articles such as pipes, window casings, siding, bottles, wall covering, and packaging film. There have been many attempts to add stabilizers to halogen-containing vinyl polymers to ameliorate the color changes that can occur in the polymer resins, particularly those color changes that occur during the first one to ten minutes of processing and/or those that occur over prolonged use.
U.S. Pat. No. 3,067,166 teaches a stabilizer for PVC comprising a mercaptoester produced by reacting a primary alcohol with alpha-mercaptopropionic acid, beta-mercaptopropionic acid, or thioglycolic acid. The stabilizer also comprises a compound of zinc or tin. U.S. Pat. No. 5,166,241 teaches a stabilizer for PVC comprising a mercaptoester and a metallic or organometallic halide. U.S. Patent Application number 2002/0103277 discloses a stabilizer composition comprising a mercaptan-containing organic compound; a tin-free metal salt such as, for example, a zinc carboxylate; and/or a Lewis acid such as boron trifluoride, aluminum chloride, zinc chloride and methyltin trichloride.
The problem addressed by the invention is therefore the provision of stabilizer compositions for halogen-containing vinyl polymers, particularly stabilizer compositions that are more effective in protecting halogen-containing vinyl polymers from degradation and discoloration during processing or long-term use.